A low-loss and compact TM-pass polarizer is demonstrated based on improved hybrid plasmonic grating (HPG) on a Z-cut lithium-niobate-on-insulator (LNOI) platform. In this work, we introduced the silica partition structures surrounding an LN (LiNbO3) ridge waveguide to support two parallel metal gratings, achieving the optimal coupling coefficient for HPG. Compared with the traditional HPG structure, the transverse electric (TE) mode suffers a higher confinement and the transverse magnetic (TM) mode transmission loss exhibits a significant reduction in the improved HPG structure. The simulation shows that the polarizer achieves a broad bandwidth of 150 nm (1500 to 1650 nm) with an extinction ratio (ER) over 20 dB and an insertion loss varying from 0.18 to 0.3 dB, including a maximum ER of 36 dB at the wavelength 1550 nm. In addition, the length of the demonstrated polarizer is only 10 μm, making it compact for integration. The proposed polarizer shows a good application prospect for integrated photonics in LNOI.
A temperature compensated three-directional double-loop strain sensor is proposed. A normal fiber Bragg grating (FBG) sensor is surface glued on double-loop titanium alloy substrate, which can improve measurement range of the sensor. The three-directional sensor is made up of three double-loop sensors in three directions so that a two-dimensional strain’s maximum strain value and direction can be detected. With a temperature compensator using a simple FBG and a temperature compensation diaphragm, temperature crosstalk is avoided and the strain sensor’s accuracy is 0.31% with measurement range of 1% (±5000 μϵ), which is seven times larger than normal FBG. In comparison with the common unidirectional strain sensor, this has great value for structural health monitoring.
A design method of a three-direction double-loop strain sensor for two-dimensional (2-D) strain is proposed and analyzed. The strain sensor is made up of three sensing arms and each arm is made of fiber Bragg gratings (FBG) sensor surface glued on titanium alloy substrate. The substrate has double loops to improve the sensor’s measurement range. The strain sensor is unique in that by designing three single arms of strain sensors in different direction, a 2-D strain’s maximum strain value and direction can be precisely determined. In comparison with common unidirectional strain sensor, this has great value for structural health monitoring. With finite element analysis and measurement demonstration, it is shown the measurement range of the strain sensor is increased by seven times compared with normal FBG sensor. The strain sensor’s measurement range can reach 1% (±5000 μϵ) with accuracy of 0.6%. An accurate and real-time monitoring system based on the sensor is presented, which demonstrated the sensor’s fast speed and high reliability.
KEYWORDS: Switching, Field programmable gate arrays, Fast packet switching, Clocks, Oscilloscopes, Control systems, Switches, Semiconductor lasers, Signal generators, Digital electronics
In order to achieve the intelligent controlling of DFB laser array, this paper presents the design of an intelligence and high precision numerical controlling electric circuit. The system takes MCU and FPGA as the main control chip, with compact, high-efficiency, no impact, switching protection characteristics. The output of the DFB laser array can be determined by an external adjustable signal. The system transforms the analog control model into a digital control model, which improves the performance of the driver. The system can monitor the temperature and current of DFB laser array in real time. The output precision of the current can reach ± 0.1mA, which ensures the stable and reliable operation of the DFB laser array. Such a driver can benefit the flexible usage of the DFB laser array.
An accurate and efficient demodulation algorithm for a fiber Bragg grating (FBG) strain sensor has been proposed and demonstrated. An accurate demodulation can be achieved by scanning only the 0.15-nm reflection spectrum of the FBG sensor instead of scanning the complete reflection spectrum. The proposed algorithm was first used to calculate the integration of 15 regions (10 pm per region) to calculate the wavelength drift. This algorithm is good in that the demodulation time can be greatly reduced without degrading the demodulation accuracy. Hence, the efficient algorithm, which can support a short demodulation time of a low-cost demodulation system, is very suitable for high demodulation rate requirements of the high-speed sensing systems.
A fiber Bragg grating (FBG) wavelength shift demodulation method based on tunable distributed feedback laser diode (DFB-LD) is proposed. A highly effective algorithm is proposed to demodulate the strain of the sensing FBG, which is scanned by the tunable DFB-LD. The system is unique in that accurate demodulation can be achieved by scanning only a 0.4-nm bandwidth FBG spectrum instead of relying on scanning the FBG’s principal power peak and the scanned spectrum can be any part of the FBG. Thus, the demodulation system is much more simplified in comparison to a traditional demodulation system, which enables using wavelength-division multiplexing for the FBG sensing network. With the strain experiment of the FBG, the results match the theory of the proposed demodulation method very well, and the errors of the strain experiment are within 2 pm. The tunable DFB-LD is based on reconstruction-equivalent chirp (REC) technology. The REC technology potentially offers a low-price, compact, and high-performance solution for the demodulation.
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